1. Field of the Invention
The present invention relates to a hadamard code generation circuit employed for a wireless communication system of a CDMA for supporting a multiplexing subscriber, and in particular, to an improved hadamard code generation circuit which is capable of extending a 48th hadamard code among orthogonal codes employed for separating channels and users of a mobile communication. And this invention can concurrently generate a 48th hadamard code and the hadamard codes higher than the 48th hadamard code.
2. Description of the Conventional Art
Generally, in order to separate channels in a CDMA communication system, a orthogonal code is used. This orthogonal is used when separating a user or modulating a signal using an orthogonal characteristic of a code. Therefore, in the CDMA communication system, an orthogonal code generator is used for generating a signal and extracting a source signal containing orthogonal code.
In addition, in order to diverse the communication service, it is needed to increase the capacity for an increasing number of subscribers. Therefore, the number of orthogonal code is increasing as user channels are increasing.
A U.S. Pat. No. 5,311,176 entitled "Walsh code generation method and apparatus" is disclosed, which is directed to generating a multiplexing code. In the patent '176, a technique for generating a 64th hadamard code is disclosed.
FIG. 1 illustrates a conventional hadamard code generation circuit which is capable of generating a 4th hadamard code and a 64th hadamard code. The operation for generating a hadamard code will be explained with reference to FIG. 1.
Two AND gates 118 and 119 receive lower 2-bit (H(1:0)) among the output signals C0 and C1 from a 2-bit counter 112 and a lowest index 2 bits of index (H(5:0)) from a 6-bit register 114 and AND the thusly received signals. A XOR-gate 124 XORs the thusly ANDed signals for thereby generating a 4th hadamard code HOUT.sub.-- L of a lower 2-bit.
In addition, a 4-bit counter 113 receives a carry-out signal from the 2-bit counter 112 and enables or disables the thusly received signal. XOR-gates 125 and 126 XOR the XOR-ed signals of AND-gates 120, 121, 122 and 123 which receive the higher 4-bit output signals (H(5:2)) among the output signals C5, C4, C3 and C2 from the 4-bit counter 113 and the MSB 4 bits of indexes from the 6-bit register 114. The XOR-gate 127 XORs the output signals from the XOR-gates 125 and 126 and a 4th hadamard code value from the XOR-gate 124 for thereby generating a 64th hadamard code HOUT.sub.-- 64.
In the conventional hadamard code generation circuit, a counter and selector are used. Then final hadamard code is generated through a binary addition operation of the mode signals selected. The counters are configured for 2-bit, 3-bit, 4-bit, 5-bit and 6-bit signals in accordance with the degree of the code. The value for selecting the output signals from the counters is determined by an index stored in a predetermined bit of register. The AND-gate multiplies the code index indicated by binary digit in the register and the output signal from the counter for thereby generating a final hadamard code by binary-summing the output values of the counters.
The 4th hadamard code will be explained.
As the elements of the hadamard matrix, "0 and 1" are used instead of "1 and -1". Therefore, the following matrix equations 1 and 2 are obtained based on "0 and 1". ##EQU1##
Equation 3 is directed to a cross matrix in which "0 and 1" are crossed with respect to H.sub.2.sup.n-1 and H.sub.2.sup.n-1.
As described above, in the orthogonal codes used for the CDMA communication system, the 4th, 8th, 16th, 32th and 64th hadamard codes are conventionally used. However, there is not disclosed a method or apparatus for concurrently generating 48th hadamard codes or 48th and 64th hadamard codes.
Therefore, as the number of subscribers is increased based on the wide range of bandwidth, the extending capability of the orthogonal codes should be increased for the increasing number of the subscribers. In the conventional orthogonal codes, it is impossible to implement an extendable hadamard code generation circuit.